Quality control has long been a necessary and routine procedure in clinical hematology. Accuracy in the counting of various types of blood cells is dependent, in part, upon the use of adequate control products and methods of using the control products. With the numerous types of equipment for particle counting now available, quality control by the use of control products is necessary, since the possibility of instrument malfunctioning is ever present. The traditional method of maintaining a quality control program for automatic particle counting equipment has consisted of providing fresh human blood as a whole blood standard. However, this fresh blood is usable for only one day, therefore, various manufactured control products which have longer product lifetime have been developed.
Commonly used particles in a control product simulate or approximate the types of particles or cells that are intended to undergo analysis. Consequently, these particles have been frequently referred to as analog particles. The analog particles should be selected or designed so that they have certain characteristics that are similar to those of the particles or cells to be analyzed in the instruments. Exemplary characteristics and parameters include similarities in size, volume, surface characteristics, granularity properties, light scattering properties and fluorescence properties.
The current state of the art of automated hematology instruments permits the user to perform a full analysis of the components of a blood sample, i.e. analysis of the hematological parameters. These parameters include, but are not limited to: white blood cell count (“WBC”), neutrophil cell percent or count (“NE %” or “NE#”), lymphocyte cell percent or count (“LY %” or “LY#”), monocyte cell percent or count (“MO %” or “MO#”), eosinophil cell percent or count (“EO %” or “EO#”), basophil cell percent or count (“BA %” or “BA#”), nucleated red blood cell percent or count (“NRBC %” or “NRBC#”), red blood cell count (“RBC”), hemoglobin concentration (“Hgb”), hematocrit (“Hct”), mean corpuscular volume (“MCV”), red blood distribution width (“RDW”), platelet count (“PLT”), mean platelet volume (“MPV”), platelet distribution width (“PDW”), platelet hematocrit (“Pct”), reticulocyte cell percent or count (“RET %” or “RET#”), mean reticulocyte volume (“MRV”) and immature reticulocyte fraction (“IRF”). Of no less importance, the functions of the hematology controls, hereinafter sometimes referred to as controls, are to ensure that the hematology analyzer itself and the reagent systems being used are operating within their specified parameters. As hematology analysis systems become more complex and provide for the analysis of additional parameters, that is parameters derived from electrical, optical and/or fluorescence analysis, appropriate controls are needed, which enable the instrument system users to also monitor the performance of these newly available parameters.
Various commercial reference control products are now available, which use various processed or fixed human or animal blood cells as analogs of human blood cells. U.S. Pat. No. 5,512,485 (to Young et al) teaches a hematology control comprising several white blood cell analogs made of processed and fixed animal red blood cells. U.S. Pat. Nos. 6,187,590 and 5,858,790 (to Kim et al) teach a hematology control comprising white blood cell analogs and a nucleated red blood cell (NRBC) analog made of lysed and fixed avian or fish red blood cells. These particles have been developed for fluorescence-based, multi-angle light scatter NRBC detection systems. U.S. Pat. Nos. 6,406,915, 6,403,377, 6,399,388, 6,221,668, and 6,200,500 (to Ryan, et al) teach a hematology control comprising a NRBC analog derived from avian blood cells. U.S. Patent Application Publication Nos. 2003/0104630 (to Ryan) teach methods of making a hematology control containing a nucleated red blood cell component by stabilizing nucleated containing blood cells, or by lysing and removing cytoplasm from blood cells. Ryan's hematology control only triggers NRBC flags on instruments, such as the Beckman Coulter STKS™ and GEN*S™ instruments.
U.S. Pat. No. 6,448,085 (to Wang et al) teaches a hematology control comprising a nucleated red blood cell (NRBC) analog derived from chicken blood and fixed human blood with nucleated red blood cells. However, these types of NRBC analogs, being fixed whole cells, significantly interfere with detection methodologies that are monitored by typical five-part differential hematology control product.
U.S. Pat. No. 5,432,089 teaches a method for preparing a reticulocyte analog by loading nucleic acid into erythrocytes using osmotic lysis techniques. However, the osmotic technology described in U.S. Pat. No. 5,432,089 only yields approximately 20% of the RBC being sufficiently “loaded” with RNA to create a reticulocyte analog. As a result, to create a moderately high level control in the range of 8–10% reticulocytes, the treated material can only be diluted 2 to 2.5 fold, which does not lend itself to an efficient manufacturing process.
Francis, et al. (U.S. Pat. Nos. 5,945,340; 5,858,789; and 5,736,402) teach methods for preparing reticulocyte analogs by arresting the maturation of natural porcine reticulocytes recovered from blood. However, porcine reticulocytes are significantly smaller than human reticulocytes, i.e. they possess a significantly lower MRV, making their reliable detection problematic on some automated hematology analyzers.
In addition, several detection methods for measuring nucleated red blood cells in a blood sample on a hematology instrument have been reported. U.S. Pat. Nos. 5,874,310 and 5,917,584 (to Li et al) generally teach a method of differentiating nucleated red blood cells by measuring two angles of light scatter signals of a blood sample under lysing condition without the requirement of using fluorescence analysis. U.S. Pat. Nos. 5,874,310 and 5,917,584 further teach a method of differentiating nucleated red blood cells by measuring light scatter and DC impedance signals. U.S. Pat. No. 6,410,330 (to Li et al) and co-pending patent application U.S. Ser. No. 10/226,800 (to Li et al) generally provide a method of determining NRBC by using DC impedance measurement.
U.S. Pat. No. 6,472,215 (to Huo et al) teaches a method of differentiating nucleated red blood cells by lysing a first aliquot and a second aliquot of a blood sample separately with a first lysing reagent system and a second lysing reagent system; measuring the first sample mixture in a flow cell by DC impedance, radio frequency, and light scatter measurements; measuring cell distributions and counting remaining blood cells in the second sample mixture by DC impedance measurements in a non-focused flow aperture; analyzing blood cell distribution patterns obtained from measuring the first sample mixture and from measuring the second sample mixture respectively; and further performing a combined analysis to differentiate NRBCs from other cell types and determine numbers of NRBCs in the blood sample.
A material that is useful in a hematology control product possesses several key properties. One important property of the material is that the material interacts with the hematology instrument and reagent system in a manner that is similar to the interaction of the patient blood sample with the hematology instrument and reagent system. In addition, the material provides a consistent and predictable result as long as the hematology analyzer and reagent system are operating within specified parameters. When the hematology analyzer and/or the reagent system are not within specified parameters, then it should be indicated by a control result that is inconsistent with the expected, predictable output. Another desirable property of a hematology control is stability. The parameter values that a user recovers when testing the control by the same method that a clinical sample would be tested, should be sufficiently stable so that the user has confidence in the control's ability to detect instrument malfunctions over a product lifespan that is sufficiently long enough to be considered economical by the user. Still another desirable property is that the method for manufacturing has a high product yield which is greater than 30% and more preferably greater than 40%.